Multiple-master DNS system

ABSTRACT

One or more embodiments provide a system and method for DNS that is resistant to losses of network connections. In some particular embodiments, DNS servers are operated to maintain consistency of DNS records between the multiple master servers in response to connection failure. Each master DNS server monitors network connectivity by periodically testing network connections of the master server (e.g., to other master servers) to determine whether the master DNS is isolated in a manner that prevents updates from being distributed between the master DNS servers. In response to detecting network isolation of the master DNS server, the master DNS server is configured to enter the isolation mode, in which the master DNS monitors the status of connections and takes appropriate actions to update and/or recover DNS data when connections are restored.

OVERVIEW

The demands on servers to provide adequate services to client devices are continuing to increase. In addition to ever increasing processing and bandwidth requirements, the number and variety of the services is also increasing. To meet these and other demands, it can be desirable to have a system that implements a number of servers that may be dynamically assigned to provide services based on user demand. These servers can be virtually identical to one another and operate in a parallel manner.

Generally, some type of mechanism is employed to assign different ones of the servers to provide services for each client connection. For example, a front-end controller can be placed in front of the servers to distribute and forward connections/services between the servers. Thus, incoming requests/connections are first received by the front-end controller. The device then distributes the workload between the servers. This arrangement works well for applications, such as a web-page server, in which successive requests by a client can be serviced by any one of the available servers. However, some online services require that successive client requests be processed by the same server. For such online services, use of a front-end controller to assign connections to different servers would require the front-end controller to maintain a mapping of the connections and servers. Maintenance of such a mapping table can create a bottleneck that frustrates linear scalability.

Another mechanism used to facilitate server assignment allows each client to select a desired server to provide the requested service. For this type of server assignment, a client retrieves a list of servers available, and then randomly selects one of the available servers from the list. This mechanism may be implemented and regulated using a Domain Name System (DNS) with multiple “A-records” and/or “service records” (SRV records, which allow for weights and priorities to be assigned to the servers). For instance, A-records contain the mapping between a domain name and an IP address. As it is possible to associate multiple IP addresses to one A-record, a service administrator can register a list of available servers in the A-record. The list of servers is provided to a client in response to a DNS query for a domain name of the service. The client then establishes a connection with a desired one of the available servers on the list. Further, this approach can be used to control load balancing between the servers by adjusting which servers are included in the list provided to the client.

DNS servers for a DNS zone are typically arranged into a hierarchy having a number of slave DNS servers, whose records are updated to match DNS records maintained by a master DNS server. Generally, a primary authoritative DNS name server in a DNS zone may accept changes to the DNS tables and respond to DNS resolution requests. Secondary authoritative DNS servers in the zone receive DNS updates from the master DNS server and do not accept changes to the DNS records. Since there is ordinarily only one primary authoritative DNS server per DNS zone, if the primary server goes down, updates to a DNS record will not be reflected in the records provided by secondary authoritative DNS servers serviced by the primary server. This can be problematic for protocols that require consistency between DNS servers.

SUMMARY

One or more embodiments are directed toward DNS control of network traffic that addresses challenges including those discussed above, and that are applicable to a variety of cellular applications, devices, systems and methods. These and other aspects of the present disclosure are exemplified in a number of implementations and applications, some of which are shown in the figures and characterized in the claims section that follows. One or more embodiments provide a system for maintaining DNS records using multiple master DNS servers.

In one embodiment, a method of operating a domain name system (DNS) is provided for use with a Voice-over-Internet Protocol (VoIP) call routing system. In particular, for use with a VoIP routing system having a domain name system (DNS) that includes at least two DNS servers in a multi-master configuration and provides dynamic DNS call routing information for setup of a VoIP call. DNS data records are updated between a first master DNS server and a second master DNS server. However, a master DNS server may become isolated from the other master DNS servers due to temporary loss of network connections. The first master DNS server monitors network connections from the first master DNS server to a wide area network. In response to detecting isolation, the first master DNS server operates in an isolation mode. The isolation mode defines rules for provision and/or updating DNS records for a plurality of DNS zones when in isolation that aids to maintain a consistent set of DNS records across the DNS system. While in the isolation mode, the first master DNS server monitors network connectivity of itself to the wide area network. The first master DNS server exits the isolation mode in response to detecting network connectivity of itself to the wide area network. In response to exiting the isolation mode, and according to the rules for the plurality of DNS zones, the first master DNS server updates DNS data records at the first master DNS server and for a first set of DNS zones using data from a second master DNS server of the DNS servers.

In another embodiment, a DNS system is provided. The system includes a plurality of slave DNS servers and a plurality of master DNS servers. The master and slave DNS servers are configured to operate in a multi-master arrangement. Each master DNS server is configured and arranged to operate in a normal mode and an isolation mode. While operating in a normal mode of operation, the master DNS server is configured to update DNS data records between the master DNS server and other ones of the plurality of master DNS servers and monitor network connections for network isolation of the master DNS server relative to a wide area network. The master DNS server is configured to enter the isolation mode in response to detecting network isolation of the master DNS server. While in the isolation mode of operation, the master DNS server is configured to monitor the network connection of the master DNS server relative to the wide area network. In response to detecting network connectivity of the master DNS server relative to the wide area network, the master DNS server is configured to update DNS records according to an isolation rule set, which indicates how DNS records are to be updated for different DNS zones, and exit the isolation mode of operation.

In yet another embodiment, a system for routing VoIP connections is provided. The system includes a plurality of VoIP processing servers and a DNS system configured to assign client connections to selected ones of the plurality of VoIP servers, the DNS system includes a plurality of slave DNS servers that are configured and arranged with a plurality of master DNS servers to operate in a multi-master arrangement. Each master DNS server is configured to operate in normal and isolation modes similar to those described above. While operating in a normal mode of operation, the master DNS server is configured to update DNS data records between the master DNS server and other ones of the plurality of master DNS servers and monitor network connections for network isolation of the master DNS server relative to a wide area network. The master DNS server is configured to enter the isolation mode in response to detecting network isolation of the master DNS server. While in the isolation mode of operation the master DNS server is configured to monitor the network connection of the master DNS server relative to the wide area network. In response to detecting network connectivity of the master DNS server relative to the wide area network, the master DNS server is configured to update DNS records according to an isolation rule set, indicating how DNS records are to be updated for different DNS zones, and exit the isolation mode of operation.

The above summary is not intended to describe each illustrated embodiment or every implementation of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure may be more completely understood in consideration of the following detailed description of various embodiments of the disclosure in connection with the accompanying drawings, in which:

FIG. 1 shows a multi-master DNS system consistent with one or more embodiments;

FIG. 2 shows a flowchart of a process for operating a master DNS server of a multi-master system, consistent with one or more embodiments;

FIG. 3 shows a flowchart of a method for performing DNS updates and recovery after restoring master and server connections in the isolation mode, consistent with one or more embodiments;

FIG. 4 shows a VoIP network system, consistent with one or more embodiments; and

FIG. 5 shows a system for server assignment and load balancing using DNS, consistent with one or more embodiments.

While the embodiments are amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit the embodiments to the particular examples described herein. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

DETAILED DESCRIPTION

Aspects of the present disclosure are believed to be applicable to a variety of different types of devices, systems and arrangements involving domain name resolution provided by DNS servers. While the present disclosure is not necessarily limited to such applications, various aspects may be appreciated through a discussion of various examples in this context. Some DNS systems implement redundancy by including multiple master DNS servers, which periodically communicate with each other to synchronize their databases (e.g., using multi-master replication). However, a master DNS server may become isolated from the other master servers due to temporary loss of network connections. In such a scenario, DNS records of the isolated server may become inconsistent with that of the other master DNS servers.

One or more embodiments provide a system and method for DNS that is resistant to losses of network connections. In some particular embodiments, DNS servers are operated to maintain consistency of DNS records between the multiple master DNS servers in response to connection failure. Each master DNS server monitors network connectivity by periodically testing network connections of the master DNS server (e.g., to other servers, including other master DNS servers) to determine whether the master DNS is isolated in a manner that may inhibit updates from being distributed between the master DNS servers. As explained in more detail below, such isolation can cause DNS records of different DNS servers to become inconsistent, which may affect operation of online services. In response to detecting failure of a network connection, a master DNS server that becomes isolated is configured to enter an isolation mode in which the master DNS monitors the status of connections and takes appropriate actions to update and/or recover DNS data when connections are restored.

For ease of reference, a master DNS server may be referred to as a master server and a slave DNS server may be referred to as a slave server. More particularly, a master server that becomes isolated due to loss of network connections may be referred to as an isolated master server herein. Also, a master server that remains connected to other master servers may be referred to as a connected master server herein.

In some embodiments, an isolated master server is configured to take different actions depending on which connection's failure caused the isolation. For instance, a master server may have several network connections including, e.g., a connection to other master servers, a connection to slave servers, and/or a connection to a reference server used to store a distributed copy of the DNS records. In one implementation, an isolated master server may be configured to perform a first set of actions in response to recovery from failure of a first combination of the connections, and perform a second set of actions in response to recovery from failure of a second combination of the connections. In some implementations, the isolated master server may be configured to enter different isolation modes in response to failure of different combinations of the connections. Each of the different isolation modes is configured to perform appropriate actions in response to recovery of the corresponding connections.

In one or more embodiments, an isolated master server may be configured to exchange DNS records with connected master servers, in response to recovery of network connections, to achieve a uniform set of DNS records across the multiple master DNS servers. Isolation of a master server may cause DNS records of the isolated master server to become inconsistent with that of the other master servers, which may adversely affect operations in various application settings. For example, if a master server becomes isolated from other ones of the master servers (connected master servers), updates received by the isolated master server may not be communicated to the connected master servers and vice-versa. For instance, in one scenario, an isolated master server may remain connected to slave servers and client applications located in a DNS zone of the isolated master and may continue to receive updates that cannot be communicated to the connected master servers until isolation is resolved.

In another scenario, the isolated master server may be isolated from slave servers and client applications in the DNS zone and thus unable to receive updates of DNS records for this zone. In such a scenario, client applications of the DNS zone may be able to submit updates to one of the connected master servers. Due to the isolation, the updates cannot be communicated to the isolated master server until connections are restored. In multi-master replication between master servers, the last of two conflicting updates should win. When isolation is resolved, updates to the DNS records should be exchanged in a manner that maintains the most recent update for each DNS record, regardless of whether the isolated or connected master server is updated. If updates are propagated from master servers down to slave servers and/or client applications before inconsistencies between DNS records are resolved, inconsistent DNS results may be provided to client applications.

In some embodiments, a master server is prevented from updating DNS records or providing updates to slave servers while operating in an isolation mode. In response to the connections of an isolated master server being restored, the server is configured to exchange DNS records with connected master servers to reestablish a uniform set of DNS records in between the master servers. After DNS records of the previously isolated master server are updated, the previously isolated master server is configured to update slave servers.

In some embodiments, an isolated master server is configured to update DNS records differently for different DNS zones once isolation is resolved. At a first master server, network connections are monitored to detect network isolation of the first server relative to a wide area network (e.g., the interne). The first master server enters an isolation mode in response to detecting network isolation of the first master server relative to the wide area network. The isolation mode defines rules for updating different DNS zones. While in the isolation mode, the first master server monitors network connections of itself relative to the wide area network. The first master server exits the isolation mode in response to detecting that network connectivity between the first master server and the wide area network has been restored. In response to exiting the isolation mode and to the rules for the plurality of DNS zones, DNS data records at the first master server are updated for a first set of DNS zones using data from the connected master servers.

In some embodiments, the isolation mode defines a set of isolation rules for updating different DNS zones. For instance, for a first isolation mode, in which a master server is isolated from the local area network, DNS data records are updated at the isolated master server for a second set of DNS zones using data from the connected master servers when connections are restored. In another isolation mode, in which the first master server remains connected to the local area network while operating in the isolation mode, DNS data records at the second master DNS server are updated for the second set of DNS zones using data from the first master DNS server when connections are restored.

FIG. 1 illustrates an example multi-master DNS hierarchy, consistent with one or more embodiments. The hierarchy includes a plurality of master DNS servers (e.g., 110, 112, and 114) connected in a multiple master arrangement in which each master DNS server maintains a redundant copy of the DNS records. The master DNS servers each write DNS updates to a reference server (e.g., 102, 104, and 106) that is used to maintain a shared redundant copy of the DNS records. The reference server allows the master servers to periodically communicate with each other to synchronize their DNS records using multi-master replication. Each of the master servers is connected to service slave servers (e.g., 120, 122, 124, 126, 128, and 130) in a respective DNS zone(s). For example, master server 110 provides DNS updates for slave servers 120 and 122 in a first DNS zone and master server 112 provides DNS updates for slave servers 124 and 126 in a second DNS zone.

As indicated above, a master server may become isolated from the other master servers due to temporary loss of network connections. In such a scenario, DNS records of the isolated server may become inconsistent with that of the other master servers. As a result, DNS records provided to slave servers may be different in the first and second DNS zones. As described in more detail below, each master DNS server monitors network connectivity of the master server (e.g., to other master servers) to determine whether the master DNS is isolated in a manner that prevents updates from being distributed between the master DNS servers and controls distribution and updates of DNS records to maintain consistency of DNS records in the DNS system.

In one or more embodiments, DNS may be used to facilitate assignment of different ones of the servers to provide services for incoming client/user connections. For instance, a DNS record for a domain name may be configured to list one or more servers available to provide the requested service to a client/user. In this example, the DNS servers may be configured to assign application servers (e.g., 132, 134, 136, and 138) to provide VoIP services for VoIP devices (e.g., 140, 142, 144, 146, and 148). Use of DNS to facilitate assignment of VoIP services to VoIP devices is discussed in more detail below with reference to FIGS. 4 and 5.

FIG. 2 shows a flowchart of a process for operating a master DNS server of a multi-master system, consistent with one or more embodiments. In a normal mode of operation at stage 202, the master server is connected to a reference server used by the master servers to store a shared copy of DNS records. The master server is also connected to other master servers, and can receive/coordinate updates with the other master servers. The master server is also connected to a number of slave servers whose DNS records are updated by the master server.

If connection to either the reference server or the other master servers is interrupted, the master server becomes isolated. If the master server becomes isolated, DNS records of the server can become inconsistent with other master servers in the system. To prevent such inconsistencies from effecting DNS operations, an isolated master server is prevented from updating DNS records or providing updates to slave servers. If slave servers were updated by the isolated master server, the DNS records may be inconsistent with records provided by DNS servers that are configured as slaves to other master servers.

While operating in the normal mode at stage 202, the master server tests connections to the reference server (server connection) and connection to other master servers (master connection) at stage 204. The testing of connections may be performed at different times in different implementations. For instance, the testing may be performed periodically at regular intervals, triggered by an event, performed at random times, etc. If either of the master or server connections is down, the master DNS server transitions into an isolation mode of operation at stage 208, in which the master DNS server does not provide DNS records to the slave DNS servers.

It is recognized that a connection may be lost between the isolation tests performed at stage 204. In some implementations, to ensure that updates and service requests are not processed by an isolated master DNS server, each master DNS server is configured to test for isolation before processing a received update or service request at stage 206. If isolation is detected at stage 206, the master DNS server transitions into an isolation mode at stage 208. Otherwise, the update or service request is processed at stage 206 and the master DNS server continues to operate in the normal mode at stage 202.

The connection to the reference servers can be tested, for example, by transmitting ISO-test packets to one or more other external servers at stage 204. For instance, in one embodiment, connection to the reference servers can be tested, for example, by transmitting ISO-test packets (e.g. ping) to external web servers (U.S. Naval Observatory Network Time Protocol (NTP) servers, www.google.com, www.uspto.gov, etc). If a response is received from any of the external web servers, the reference server connection is determined to be operational. Otherwise, the connection to the reference server is determined to be unavailable. The connection with other master servers may be tested in a similar manner. It is recognized that various implementations may utilize any number of other methods for testing of network connections that are known in the art. The different methods of testing network connections may be used alone or in combination. If the server connection and master connection are both determined to be available, the master server continues to operate in the normal mode at stage 202. Otherwise, if either the server connection or the master connection is determined to be unavailable, the master server enters the isolation mode at stage 208.

While operating in the isolation mode, the master server does not provide or update DNS records unless sufficient connections are available to coordinate with other master servers to ensure that DNS records do not become inconsistent. Provision and updating of DNS records in the isolation mode are discussed in more detail below with reference to TABLE 1.

The master server performs isolation tests at stage 212 to detect when master and server connections have been restored. As discussed with reference to testing stage 204, isolation tests in stage 212 may be performed at regular intervals, triggered by an event, performed at random times, etc. Once master and server connections have been restored, any queued updates can then processed by the master server at stage 214 according to the isolation rules. Updates that have been performed by other master servers are also retrieved at stage 214. Once record updates have been completed, slave DNS servers of the master DNS server are updated at stage 216.

As indicated above, in some embodiments, the update and recovery process may be different depending on the connections of the isolated master DNS server. TABLE 1 shows some different connection scenarios that may be encountered in one or more implementations. For ease of reference, the respective update and recovery process for each different combination of network connections of the master server are described as a different isolation mode. Various embodiments of the present disclosure are directed toward the use of different rules based upon the particular isolation mode. These rules can define how the master DNS server operates while in isolation mode as well as how the master DNS server recovers once the isolation mode is exited. Moreover, the rules can define how the master server handles transitions between the different isolation modes. It is understood that various embodiments may be implemented to operate using any number of isolation modes. For ease of explanation, embodiments and examples are primarily described with reference to a master server is configured to operate in three different isolation modes shown in TABLE 1.

For instance, the master server may operate in isolation mode 1 in response to any number of different potential problems with the connection to the reference server. For instance, it may be that one or more of the reference servers has a local problem (e.g., is subject to a denial-of-service (DOS) attack or is down for maintenance). In other instances, there may be a wider problem with Internet connectivity. This could also signify that the local Internet connection is unreliable. Thus, it may be that the master DNS server is currently subject to a DOS attack or has another issue associated with Internet connectivity. This can result in intermittent failures and successes for connection tests for both reference servers and other master DNS servers. The master server may transition from isolation mode 1 to isolation mode 2 in response to encountering similar problems with the connections to other master servers. The master server may transition from isolation mode 2 to isolation mode 3 in response to encountering similar problems with the connections to the slave servers.

Isolation rules associated with each isolation mode may direct how the master server operates in each of the different isolation modes. For instance, in some embodiments, the rules may specify that a master server operating in any of isolation mode 1, 2, and 3 will not update DNS records until and unless a successful connection has been established with the other master servers as well as the reference server. Alternatively or in addition, the rules may specify that a master server operating in isolation mode 1 will communicate to slave servers that a DNS record is invalid if another master server indicates that the record has been updated in the reference library. In such embodiments, the master server operating in modes 2 or 3, in which the master server is isolated from other master servers, will not provide DNS records to slave servers because it cannot be determined whether the records have been updated by another master server.

The update and recover rules can also differ depending on whether the connection to slave DNS servers or local applications was lost. For instance, if an isolated master DNS server has a connection to slave DNS servers and local applications, the master DNS server can receive and queue the requests for later updating. However, if local applications are unable to establish a connection with the isolated master DNS server, update requests may be sent to another master DNS server. In the former scenario, the update and recovery process should update DNS records for the local zone using the queued records from the previously isolated master DNS server. In the later scenario, the update and recovery process should update DNS records for the local zone using records from the other master DNS servers.

TABLE 1 Connection to Connection to Other Master Connection to Connection Reference Server DNS Servers Local Slave Scenario (server connection) (master connection) DNS Servers Normal Mode Connected Connected Connected Isolation 1 No connection Connected Connected Isolation 2 No connection No connection Connected Isolation 3 No connection No connection No connection

FIG. 3 shows a flowchart of a method for performing DNS updates and recovery after restoring master and server connections in the isolation mode. DNS record updates for non-local zones are retrieved from other master DNS servers at blocks 302 and 304. One of the other master DNS servers is selected at block 302. Updates from the selected DNS server are retrieved at block 304. If the isolated server was isolated from slave servers at decision block 306, updates for local DNS zones are retrieved from the selected master server at block 316. Otherwise, local DNS zone records are updated using data of the isolated master DNS server at blocks 308-312. Update requests queued at the isolated master DNS server are sent to the selected master at block 308. Local update requests are sent to each additional master DNS server at blocks 310 and 312. After DNS records of the master DNS servers have been updated, records of slave DNS servers are updated at block 314.

For some online services, it may be desirable to dynamically adjust which servers are assigned to service a particular client connection. For instance, in voice-over-IP (VoIP) applications, server selection is based on the current availability of servers and latency of connections among the available servers. Depending on network conditions, geographic location of clients and servers, and server load, a list of servers provided to clients by DNS may need to be frequently updated to reflect the changes in server load and connection latency. However, unlike many online services such as web-servers, VoIP services need to be synchronized between multiple clients who are located in separate geographic locations. Due to such geographic separation, different clients may retrieve DNS queries from different DNS servers. Inconsistencies between these different DNS servers can inhibit the ability to provide effective VoIP services to users.

The multi-master DNS system is believed to be applicable to a number of different applications that require consistency of records in the DNS system. However, for ease of explanation, the embodiments and examples are primarily described with reference to VoIP applications herein. FIG. 4 shows a VoIP network configured in accordance with one or more embodiments. The VoIP network includes a number of VoIP client/user devices (404, 408, 414, 422, and 426) and a number of VoIP servers (e.g., 412 and 424). In response to a VoIP device request, the VoIP servers are configured to facilitate creation of a VoIP connection between two of the VoIP devices. In some embodiments, a VoIP server may also be configured to facilitate VoIP communication between a VoIP device and a plain old telephone system (POTS) 418 of a PSTN network 416 that is connected to the internet 430 via a gateway 420. As indicated above, and explained in more detail with reference to FIG. 5, VoIP connections may be assigned to VoIP servers using a DNS system. As discussed with reference to FIGS. 2 and 3, the DNS system includes DNS servers (e.g., 402 and 410) connected in a multi-master configuration. As discussed above, the DNS servers are configured to store updated DNS records in a distributed reference server (e.g., 406 and 428) that is shared by the master DNS servers of the DNS system.

As indicated above, DNS may be used to assign different ones of the servers to provide services for incoming client connections. A list of available servers can be provided to clients using DNS A-records or SRV records. A-records contain the mapping between a domain name and an IP address. As it is possible to associate multiple IP addresses to one A-record, a service administrator can register a list of available servers in the A-record. The list of servers is provided to a client, in response to a DNS query for a domain name of the service. The client then establishes a connection with a desired one of the available servers on the list. By adjusting which servers are included in the list provided to the client, server assignment can be adjusted for load-balancing and latency adjustment.

FIG. 5 shows a system for server assignment and load balancing using DNS, consistent with one or more embodiments. Client devices 502 represent a number of different communication devices that connect to network 504. Non-limiting examples include home computers, cell phones, personal digital assistants (PDAs), television receivers, laptops, and Voice over Internet Protocol (VoIP) devices. FIG. 5 shows communication flow between the client devices 502, the servers 506, and a weight/subset determination device 514. The vertical arrows represent communications between devices. These arrows are arranged to show an example sequence of communication events between devices with the first communications occurring on the left and the last communications occurring on the right. The communication events to the left of the first dotted line represent an initial connection client request and DNS server response. The response may, for instance, indicate a list of servers available to provide the requested service.

The center communication event, located between the dotted lines, represents a client request for a specific server. The bi-directional communication event, located on the right, represents the fulfillment of the client requested service/connection. The first communication shown is a client request 510 for services from (and/or connections to) the servers 506. In response to this request, the weight/subset determination device 514 determines and provides connection information to the requesting client device. This connection information can include weight values 512 for the servers that may be used to influence client selection of particular servers. By adjusting the servers included in the list and/or adjusting the weight values assigned to each server in the list, assignment of connections to the servers can be adjusted. Alternatively or in addition, the list may include other data for each server such as available processing resources, current processing load, latency, etc.

Once the client has selected a server, the client sends a connection request 516 that specifies the selected server. The selected server responds to the client request and a connection is then established between the selected server and the requesting client device. This connection can be used to provide a variety of desired client-server services 518.

According to one embodiment, weight/subset determination device 514 is implemented using a dedicated processor, server, circuit, or device. Such a device can be assigned to handle all incoming requests from clients 502. In this manner, the servers 506 are free from handling this portion of the process. This allows for the device 514 to be located in physically different locations from one or more of the servers 506. In certain embodiments, device 514 can be implemented using a plurality of separate servers, processors, circuits, or devices. In this manner, the client requests can be distributed so as not to have single point of failure or a bottleneck. Various other configurations of devices are possible, such as a device that also serves as a gateway or router for one or more of the servers 506.

These and other aspects can be implemented in a number of different manners including, but not limited to, stored executable data, computer processors, programmable logic, hardware circuit logic and combinations thereof. The various embodiments described above are provided by way of illustration only and should not be construed to be limiting. Based upon the above discussion and illustrations, those skilled in the art will readily recognize that various modifications and changes may be made without strictly following the exemplary embodiments and applications illustrated and described herein. For example, the methods, devices, and systems discussed herein may be implemented in connection with voice-over Internet services, streaming media and call processing. Some various embodiments may also be implemented using a variety of approaches such as those involving a number of different operating systems and software programs/packages. Such modifications and changes do not depart from the true spirit and scope of the envisioned embodiments, including that set forth in the following claims. 

What is claimed is:
 1. A method for operating a domain name system (DNS) in a Voice-over-Internet Protocol (VoIP) call routing system, the DNS including at least two DNS servers in a multi-master configuration that provides dynamic DNS call routing information for setup of a VoIP call, the method comprising, at a first master DNS server of the at least two DNS servers: updating DNS data records between the first master DNS server and a second master DNS server of the at least two DNS servers; monitoring for network isolation of the first master DNS server relative to at least one wide area network; entering an isolation mode in response to detecting network isolation of the first master DNS server of the at least two DNS servers, the isolation mode defining rules for a plurality of DNS zones; monitoring, while in the isolation mode, for network connectivity of the first master DNS server relative to the wide area network, wherein the steps of monitoring include attempting to access a plurality of remote websites; exiting the isolation mode in response to detecting network connectivity of the first master DNS server relative to the wide area network; updating, in response to exiting the isolation mode and to the rules for the plurality of DNS zones, DNS data records at the first master DNS server and for a first set of DNS zones using data from the second master DNS server of the least two DNS servers; at the first master DNS server, processing DNS update requests received in the first set of DNS zones; and at the second master DNS server, processing DNS update requests received in a second of the plurality of DNS zones.
 2. A method for operating a domain name system (DNS) in a Voice-over-Internet Protocol (VoIP) call routing system, the DNS including at least two DNS servers in a multi-master configuration that provides dynamic DNS call routing information for setup of a VoIP call, the method comprising, at a first master DNS server of the at least two DNS servers: updating DNS data records between the first master DNS server and a second master DNS server of the at least two DNS servers; monitoring for network isolation of the first master DNS server relative to at least one wide area network; entering an isolation mode in response to detecting network isolation of the first master DNS server of the at least two DNS servers, the isolation mode defining rules for a plurality of DNS zones; monitoring, while in the isolation mode, for network connectivity of the first master DNS server relative to the wide area network; exiting the isolation mode in response to detecting network connectivity of the first master DNS server relative to the wide area network; updating, in response to exiting the isolation mode and to the rules for the plurality of DNS zones, DNS data records at the first master DNS server and for a first set of DNS zones using data from the second master DNS server of the least two DNS servers; and monitoring for network isolation relative to a local area network that includes one or more DNS servers configured as slaves to the first master DNS server, the one or more DNS servers being in the first set of DNS zones, and wherein the rules for the plurality of DNS zones specify how DNS data records are updated based upon whether or not the local area network is isolated from the first master DNS server.
 3. The method of claim 2, further including: in response to exiting the isolation mode and the first master DNS server being isolated from the local area network while operating in the isolation mode, updating DNS data records at the first master DNS server for a second set of DNS zones using data from the second master DNS server; and in response to exiting the isolation mode and the first master DNS server being connected to the local area network while operating in the isolation mode, updating DNS data records at the second master DNS server for the second set of DNS zones using data from the first master DNS server.
 4. The method of claim 3, further including: in response to exiting the isolation mode, updating DNS data records at the first master DNS server for a third set of DNS zones using data from the second master DNS server, regardless of whether the first master DNS server is isolated from the local area network while operating in the isolation mode.
 5. The method of claim 1, further comprising, at the second master DNS server: updating DNS data records between the first master DNS server and the second master DNS server of the at least two DNS servers; monitoring for network isolation of the second master DNS server relative to at least one wide area network; entering the isolation mode in response to detecting network isolation of the first master DNS server of the at least two DNS servers, the isolation mode defining rules for the plurality of DNS zones; monitoring, while in the isolation mode, for network connectivity of the second master DNS server relative to the wide area network; exiting the isolation mode in response to detecting network connectivity of the second master DNS server relative to the wide area network; updating, in response to exiting the isolation mode and to the rules for the plurality of DNS zones, DNS data records at the second master DNS server and for a second set of DNS zones of the plurality of DNS zones using data from the first master DNS server; and providing, in response to exiting the isolation mode and to the rules for the plurality of DNS zones, DNS data records to the first master DNS server for updating the first set of DNS zones that are different from the second set of DNS zones.
 6. The method of claim 1, further comprising, at a slave DNS server in the first set of DNS zones, the slave DNS server being a slave to the first master DNS server: updating DNS data records from the first master DNS server; and in response to the first master DNS server operating in the isolation mode, updating DNS data records from the second master DNS server.
 7. A method for operating a domain name system (DNS) in a Voice-over-Internet Protocol (VoIP) call routing system, the DNS including at least two DNS servers in a multi-master configuration that provides dynamic DNS call routing information for setup of a VoIP call, the method comprising, at a first master DNS server of at least two DNS servers: updating DNS data records between the first master DNS server and a second master DNS server of the at least two DNS servers; monitoring for network isolation of the first master DNS server relative to at least one wide area network; entering an isolation mode in response to detecting network isolation of the first master DNS server of the at least two DNS servers, the isolation mode defining rules for a plurality of DNS zones; monitoring, while in the isolation mode, for network connectivity of the first master DNS server relative to the wide area network; exiting the isolation mode in response to detecting network connectivity of the first master DNS server relative to the wide area network; updating, in response to exiting the isolation mode and to the rules for the plurality of DNS zones, DNS data records at the first master DNS server and for a first set of DNS zones using data from the second master DNS server of the least two DNS servers; the first master DNS server is located in a first data center and the second master DNS server is located in a second data center; and the updating of the DNS data records between the first master DNS server and a second master DNS server includes updating DNS data records in one or more reference severs communicatively coupled to the first and second master DNS servers.
 8. A DNS system, comprising: a plurality of slave DNS servers; a plurality of master DNS servers configured and arranged with the plurality of slave servers in a multi-master arrangement, each master DNS server being configured and arranged to, while in a normal mode of operation: update DNS data records between the master DNS server and other ones of the plurality of master DNS servers; monitor network connections of the master DNS server for network isolation of the master DNS server relative to at least one wide area network; and enter an isolation mode of operation in response to detecting network isolation of the master DNS server; and while in the isolation mode of operation: monitor the network connection of the master DNS server relative to the wide area network; in response to detecting network connectivity of the master DNS server relative to the wide area network, update DNS records according to an isolation rule set indicating how DNS records are to be updated for different DNS zones; and exit the isolation mode of operation; wherein the isolation rule set causes the master DNS server to perform the updating of DNS data records for a first set of DNS zones according to a first rule set and for a second set of DNS zones according to a second rule set.
 9. The system of claim 8, wherein the first rule set causes the master DNS server to update DNS records at the master DNS server for the first set of DNS zones using data from a different one of the plurality of master DNS servers; and the second rule set causes the master DNS server to: in response to the master DNS server being isolated from slave DNS servers in the second set of DNS zones when entering the isolation mode, update DNS records at the master DNS server for the second set of DNS zones using data from the different one of the plurality of master servers; and in response to the master DNS server being connected to slave DNS servers in the second set of DNS zones when entering the isolation mode, update DNS records at the other ones of the plurality of master DNS servers for the second set of DNS zones using data from the different one of the plurality of master servers.
 10. The system of claim 9, wherein ones of the plurality of slave DNS servers in the second set of DNS zones are configured and arranged to: retrieve DNS updates with the master DNS server in response to the master DNS server being connected to the ones of the plurality of slave DNS servers; and retrieve DNS updates with a different one of the master DNS servers in response to the master DNS server being isolated from the ones of the plurality of slave DNS servers in the second set of DNS zones.
 11. A DNS system, comprising: a plurality of slave DNS servers; a plurality of master DNS servers configured and arranged with the plurality of slave servers in a multi-master arrangement, each master DNS server being configured and arranged to, while in a normal mode of operation: update DNS data records between the master DNS server and other ones of the plurality of master DNS servers; monitor network connections of the master DNS server for network isolation of the master DNS server relative to at least one wide area network; and enter an isolation mode of operation in response to detecting network isolation of the master DNS server; and while in the isolation mode of operation: monitor the network connection of the master DNS server relative to the wide area network; in response to detecting network connectivity of the master DNS server relative to the wide area network, update DNS records according to an isolation rule set indicating how DNS records are to be updated for different DNS zones; exit the isolation mode of operation; and wherein each of the plurality of master DNS servers is configured to perform the monitoring of the network connections of the master server for network isolation of the master DNS server relative to at least one wide area network by monitoring network connections of the master DNS server for network isolation of the master DNS server relative to at least one wide area network.
 12. A system for routing VoIP connections, comprising: a plurality of VoIP processing servers; and a DNS system configured to assign client connections to selected ones of the plurality of VoIP processing servers, the DNS system including a plurality of slave DNS servers configured and arranged with a plurality of master DNS servers to operate in a multi-master arrangement, each master DNS server being configured and arranged to, while in a normal mode of operation: update DNS data records between the master DNS server and other ones of the plurality of master DNS servers; monitor network connections of the master DNS server for network isolation of the master DNS server relative to at least one wide area network; and enter an isolation mode of operation in response to detecting network isolation of the master DNS server; and while in the isolation mode of operation: monitor the network connection of the master DNS server relative to the wide area network; in response to detecting network connectivity of the master DNS server relative to the wide area network, update DNS records according to an isolation rule set indicating how DNS records are to be updated for different DNS zones; and exit the isolation mode of operation; and wherein each of the plurality of master DNS servers is configured to perform the monitoring of the network connections of the master DNS server for network isolation of the master DNS server relative to at least one wide area network by monitoring network connections of the master server for network isolation of the master DNS server relative to at least one wide area network.
 13. The system of claim 12, wherein the isolation rule set causes the master DNS server to: perform the updating of DNS data records for a first set of DNS zones according to a first rule set; and perform the updating of DNS data records for a second set of DNS zones according to a second rule set.
 14. The system of claim 13, wherein the first rule set causes the master DNS server to update DNS records at the master DNS server for the first set of DNS zones using data from a different one of the plurality of master DNS servers; and the second rule set causes the master DNS server to: in response to the master DNS server being isolated from slave DNS servers in the second set of DNS zones when entering the isolation mode, update DNS records at the master DNS server for the second set of DNS zones using data from the different one of the plurality of master servers; and in response to the master DNS server being connected to slave DNS servers in the second set of DNS zones when entering the isolation mode, update DNS records at the other ones of the plurality of master DNS servers for the second set of DNS zones using data from the different one of the plurality of master servers.
 15. The system of claim 14, wherein ones of the plurality of slave DNS servers in the second set of DNS zones are configured and arranged to: retrieve DNS updates with the master DNS server in response to the master DNS server being connected to the ones of the plurality of slave DNS servers; and retrieve DNS updates with a different one of the master DNS servers in response to the master DNS server being isolated from the ones of the plurality of slave DNS servers in the second set of DNS zones.
 16. The system of claim 13, wherein each master DNS server is further configured and arranged to monitor network connections for network isolation of the master DNS server relative to a local area network that includes one or more DNS servers configured as slaves to the master DNS server, one or more DNS servers being in the first set of DNS zones, and wherein the first and second rule sets for the DNS zones specify how DNS data records are updated based upon whether or not the local area network is isolated from the master DNS server.
 17. The system of claim 15, wherein each master DNS server is further configured and arranged to: in response to exiting the isolation mode and the master DNS server being isolated from a local area network while operating in the isolation mode, update DNS data records at the master DNS server for the second set of DNS zones using data from another one of the master DNS servers; and in response to exiting the isolation mode and the master DNS server being connected to the local area network while operating in the isolation mode, update DNS data records at the second master DNS server for the second set of DNS zones using data from the master DNS server. 